1. Field of the Invention
This invention relates to improved mesh for removing entrained or suspended droplets or particulates in a gas stream.
2. The State of the Art
Many chemical and other industrial processes create a gas stream that includes solid and/or liquid particles that must be removed from the gas stream. These particles are typically liquid droplets created by entrainment, impingement, chemical reaction, or condensation, but can also be solid particles.
Perhaps the most typical of methods for removing these unwanted particles is a device which causes the gas/particle flow to change direction. Because the particle has a higher density than the gas of the stream, the momentum of the particle will tend to make the particle travel in a straight line and not change direction as quickly as the gas. For example, in the case of a stream of water droplets in air, the gas stream can be passed through a wire mesh: the liquid droplets cannot negotiate the tortuous path through the mesh and so they land on and adhere to the mesh, and coalesce, by surface tension, and then run off from the mesh due to gravity. Gas-liquid separations that use demisting pads include gas plants, refineries, steam-generating power plants, gas scrubbers, and various other operations used in producing petrochemicals and speciality chemicals.
Another device typically used for removing liquid or solid particles from a gas stream includes a series of wave plates (vanes) arranged parallely, each vane being a thin sheet that is formed into hills and valleys. The vanes are arranged spaced closely together. The gas stream enters one side and takes a zig-zag path to reach the other side. The entrained droplets cannot negotiate the rapid zig-zag and impinge on the vane, where they cling and run down the wall. While vanes are more robust, they are significantly heavier and more costly to manufacture than a wire mesh mist collector.
The typical industry standard for mesh pads is to use 0.011 inch wire at a density of 9 lb./ft3. The wire commonly used is 304SS, or any suitable alloy, metal, or plastic chemically compatible with the process stream. Some operations use a multilayered pad having the lowest density pad upstream and the highest density pad downstream. Although termed “multilayered,” the pad actually has multiple zones, where each zone is comprised of one or more layers of the same mesh. Multilayer pads presently used in the industry have two or three zones at most. The pad must remove entrained material but without causing any significant pressure drop. In a typical plant, a pressure drop of one inch of water across a pad amounts to hundreds of thousands of dollars a year in a one billion SCF/d plant to push the gas around with the increased pressure drop.